Chapter 9: Error Handling

src/main.rs

@@ -10,6 +10,7 @@ fn main() {
     chapter_6();
     chapter_7();
     chapter_8();
+    chapter_9();
 }
 
 fn chapter_1() {
@@ -996,3 +997,44 @@ fn hash_maps() {
 
     println!();
 }
+
+fn chapter_9() {
+    unrecoverable_errors_with_panic();
+    recoverable_errors_with_result();
+    panic_or_result();
+
+    println!();
+}
+
+fn unrecoverable_errors_with_panic() {
+    println!("The `panic!` macro crash the program gracefully. We may configure it to abort instead.");
+    println!("If we want the stacktrace we need to set the environment variable: `RUST_BACKTRACE`.");
+
+    println!();
+}
+
+fn recoverable_errors_with_result() {
+    println!("The `Result` enum enable a function to return a recoverable error.");
+    println!("We may check for a kind of error by stacking the `match`.");
+    println!("Instead we may prefer to use closures to better communicate our intention and not use to much nested `match`.");
+    println!("For example `unwrap` and `expect` are shortcuts to panic on error.");
+    println!("See chapter 13 for more infos.");
+
+    println!("If we want to let the caller take care of the errors we encounter we can propagate the error with `?`");
+    println!("Fun example (ending with a bit of a cheat): https://doc.rust-lang.org/stable/book/2018-edition/ch09-02-recoverable-errors-with-result.html#propagating-errors");
+
+    println!();
+}
+
+fn panic_or_result() {
+    println!("It is ok to panic! when in `Examples, Prototype Code, and Tests`");
+    println!("For the examples and when prototypying `unwrap` and `expect` are clear markers showing where to handle the errors");
+    println!("When testing panicking is the way to tell that the test failed");
+
+    println!("When we hardcode a value (or have more infos than the compiler)");
+    println!("We can also panic when the developper using our library break one of our contract.");
+    println!("Each time we create contract like this we should document them.");
+    // Example: Trying to access an array/Vec<> after a it's max length (out-of-bounds)
+
+    println!();
+}